Anesthesiology
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The diffusion dynamics of intravitreal gas bubbles injected during retinal reattachment procedures were studied using a mathematical model. This model predicts the effect of 70 per cent nitrous oxide anesthesia on the volume of the intravitreal bubble. The calculations indicate that when 70 per cent nitrous oxide administration is continued following intravitreal gas injection, there is a rapid, almost threefold increase in the volume of the injected bubble. ⋯ The two major factors that influence intravitreal bubble volume are the mixture of air or SF6 injected and the pattern of nitrous oxide use during anesthesia. These factors can be controlled. The importance of bubble volume changes on intraocular pressure and retinal blood flow also depend on other factors such as scleral rigidity, blood pressure, the presence of glaucoma, and the size of the injected gas bubble relative to the total vitreal volume.
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Anesthesiologists from 65 institutions participated in a multicenter study to assess the efficacy of lyophilized intravenous dantrolene sodium in treating anesthetically related malignant hyperthermia (MH). Of 21 patients treated with the drug, eight were judged to have unequivocal MH and were treated according to study protocol. Three were judged to have probable MH and were also treated according to study protocol. ⋯ All survived and had no adverse drug reactions. Dantrolene therapy resulted in a statistically significantly lower mortality rate than would be expected in MH patients. The study supports animal data suggesting that dantrolene is specific in reversing MH.
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Comparative Study
Different laryngeal responses during respiratory arrest produced by hypoxia withdrawal, thiopentone, ketamine, and lidocaine in cats.
The changes in laryngeal resistance (LR) during respiratory arrest produced by withdrawal of hypoxia stimulation and administration of various respiratory depressants were studied in 14 spontaneously breathing, anesthetized cats (11 cats with alpha-chloralose and three cats with halothane). Withdrawal of hypoxia stimulation caused a transient respiratory arrest with no central inspiratory activity, during which a considerable increase in LR was observed to a level higher than the fixed resistance after muscle paralysis [LR(fix)]. Intravenous injection of thiopentone, ketamine, and lidocaine all caused a transient respiratory arrest. ⋯ Ketamine maintained a dilatation of the larynx, and LR during ketamine-induced respiratory arrest was lower than LR(fix). Lidocaine caused a constriction of the larynx and LR greatly increased, leading frequently to laryngospasm. These results indicate that hypoxia withdrawal, thiopentone, ketamine, and lidocaine all cause different effects on the central inspiratory activity, and that the central respiratory depression produced by these methods is not accompanied by a uniform depression of laryngeal function.